The present disclosure refers to the electronic technical field, especially a PCB (printed circuit board) Rogowski coil.
A Rogowski coil is the one formed by uniformly winding a wire on a frame made of a nonmagnetic material with uniform section. The Rogowski coil, featured with light weight, wide frequency band and good linearity and no magnetic saturation, has been universally used in a current measuring device. According to whether the Rogowski coil can be opened during measurement, it can be divided into two types, i.e., a closed Rogowski coil and an opened Rogowski coil. The closed Rogowski coil is shown in FIG. 1.
The closed Rogowski coil 100 includes the following parts:
(1) Signal output end 125 and signal output end 130
(2) Ring winding 110 wound from signal output end 130 to the end of ring winding 120
(3) Return wire turn 155 from the end of ring winding 120 to signal output end 125 along the center of ring winding
When the closed Rogowski coil 100 is used for current measurement, a current-carrying conductor 105 is required to pass through the closed Rogowski coil 100 first. The current-carrying conductor 105 is required to pass through the center of the closed Rogowski coil 100 vertically with the centers of the current-carrying conductor 105 and closed Rogowski coil 100 in superposition to ensure measurement accuracy. The current-carrying conductor 105 is surrounded by the closed Rogowski coil 100. When the alternating current I(t) to be measured flows through the current-carrying conductor 105, it generates an AC magnetic field around the current-carrying conductor, and the magnetic lines are approximated as the circle centered in the center of current-carrying conductor 105. Centers of various cycles of wire turns of the ring winding 110 for closed Rogowski coil 100 are in one of the circular magnetic lines. The sectional areas corresponding to various wire turns of the ring winding 110 for closed Rogowski coil 100 are equal. Each wire turn section direction of the ring winding 110 is in line with the normal direction of magnetic lines (i.e., radius direction of the section center is pointing to the center of the current-carrying conductor 105), and is vertical to the tangential direction of the circular magnetic lines. Therefore, the magnetic flux φi(t) of each ring winding wire turn of the closed Rogowski coil is ensured to be approximately equal with the magnetic flux in direct proportion to the current.Φi(t)=L·I(t)  (1)
The alternating current I(t) to be measured causes the change on magnetic flux within the volume encircled by the ring winding of the closed Rogowski coil 100, which can be converted into voltage signals in proportion to differential of the total magnetic flux by the closed Rogowski coil 100, i.e. the output voltage signal V(t) between output ends 125 and 130 of the closed Rogowski coil 100.
                              V          ⁡                      (            t            )                          =                              -                                          d                ⁢                                                                              dt                                ⁢                                    ∑              t                        ⁢                                          Φ                i                            ⁡                              (                t                )                                                                        (        2        )            
After simplification, the output voltage signal V(t) of the closed Rogowski coil is approximately in proportion to the differential of alternating current I(t).
                              V          ⁡                      (            t            )                          =                              -            M                    ·                                    dI              ⁡                              (                t                )                                      dt                                              (        3        )            
Signals in proportion to alternating current I(t) can be acquired from the integral of output voltage signal V(t) of the closed Rogowski coil, which is the theory for the closed Rogowski coil to measure alternating current.I(t)=K·∫V(t)dt  (4)
As the closed Rogowski coil has high accuracy for current measurement and big bandwidth for measuring signal, it achieves the measurement by electric isolation at low cost, and its current withstanding capacity is almost infinite. The closed Rogowski coil is used in accurate current measurement of current-carrying conductor with permanent position, which has application in fields such as relay protection, etc.
During the current measurement conducted by the closed Rogowski coil 100, the ring winding 110 picks up not only the magnetic variation of alternating current I(t) to be measured, but also other AC interfering magnetic fields in the space. For example, when the AC interfering magnetic field vertical to the page direction in FIG. 1 occurs, voltage signal will be generated between the starting point 130 and ending point 120 of the ring winding 110.
In order to reduce the influence on the measurement by the closed Rogowski coil 100 from the external magnetic field, besides the ring winding 110 of the closed Rogowski coil 100, a cycle of return wire turn 115 will be wound between the ending point 120 and signal output end 125 of the ring winding 110 along the circle centered in center of the ring winding 110. Thus, when the AC interfering magnetic field vertical to page direction in FIG. 1 occurs, the voltage signal will be generated between the starting point 120 and ending point 125 of the return wire turn 115 by the AC interfering magnetic field. The voltage signal and the voltage signal between the starting point 130 and ending point 120 of the ring winding 110 are approximately equal in size and opposite in polarity with signal superposition result of approximately zero. Therefore, when the AC interfering magnetic field vertical to the page direction in FIG. 1 occurs, almost no interfering voltage signal will be generated between the output ends 125 and 130 of the closed Rogowski coil 100.
The traditional closed winding Rogowski coil, shown in FIG. 2, is formed through the winding on framework made of the circular non-magnetic conducting material, including the ring winding and the return wire turn. During the winding, the ring winding is wound after a cycle of return wire turn is placed in the center of the circular framework. The voltage signal generated by the external interfering magnetic field on ring winding of the closed Rogowski coil is approximately equal in size to the voltage signal generated on return wire turn but is opposite in polarity. Therefore, with signal superposition resulting in approximately zero, it reduces the influence of external magnetic field on measurement conducted by the closed Rogowski coil.
As the winding of the traditional closed winding Rogowski coil is generally completed by manual work or winding machine, it is hard to achieve uniform winding coil or equal cross section of each coil turn. The traditional closed winding Rogowski coil has the disadvantage of easy disconnection, large capacitance increase error, etc., so the parameter consistency during the industrial production is hard to be guaranteed. As a result, the characteristics of Rogowski coil during current measurement are affected.
A new type of closed Rogowski coil, called closed PCB Rogowski coil for short, is made from PCB to overcome the disadvantages of traditional closed Rogowski coil. See the circular closed PCB Rogowski coils 305 and 310 in FIG. 3. The closed PCB Rogowski coil is adopted with computer aided design (CAD), which means the printed wire (hereafter called wiring) is uniformly arranged on the PCB. See closed PCB Rogowski coil 305 in FIG. 3. A cycle of wire turn on the ring winding of closed PCB Rogowski coil 305 is composed of wiring 315 on the top layer (the top layer of PCB is the PCB surface which faces the reader, and the bottom layer is in opposite direction of the top layer), with plated through hole (hereafter called through hole for short) 320 connecting with the top layer and bottom layer and the wiring 325 on the bottom layer. Each wire turn cycle of the closed PCB Rogowski coil 305 is in radius direction from the center of circular PCB and is uniformly arranged along the circle with the section of the wire turn vertical to PCB.
As better digital processing technology being adopted for the PCB, the equality of section area on each wire turn cycle of the closed PCB Rogowski coil is ensured in the technological aspect. The produced closed PCB Rogowski coil not only overcomes the disadvantages of traditional closed Rogowski coil, but also enjoys optimized sensitivity, measurement accuracy and performance stability as compared to the traditional coil wound by copper wire. The production of closed PCB Rogowski coil is convenient and rapid, because it only needs to draw the wiring diagram on the computer. The closed PCB Rogowski coil is produced by numerical control machine tool to avoid the tedious process of winding, which shortens the coil processing cycle and improves the production efficiency. The variance of the closed PCB Rogowski parameter is small during mass production, and therefore, the performance parameters of coils from the same production batch are basically the same.
When the closed PCB Rogowski coil 305 is used for current measurement, besides the magnetic variation of alternating current I(t) to be measured, the ring winding also picks up other AC interfering magnetic fields in the space. For example, when the AC interfering magnetic field vertical to page direction in FIG. 3 occurs, interfering voltage signal is generated between the output ends 345 and 350 of the closed PCB Rogowski coil 305. In order to reduce the influence on measurement of closed PCB Rogowski coil 305 caused by the external magnetic field, the two series-connected PCBs on the closed PCB Rogowski coil can be adopted to form a combined PCB closed Rogowski coil. FIG. 3 shows the series connection of closed PCB Rogowski coil 305 and closed PCB Rogowski coil 310, which forms the combined PCB closed Rogowski coil 300.
The wirings of closed PCB Rogowski coil 310 and closed PCB Rogowski coil 305 are arranged in a mirror image method with the wiring of ring winding in opposite direction. A wire turn cycle of the closed PCB Rogowski coil 310 is composed of wiring 330 on the bottom layer, the through hole 335 and wiring 340 on the top layer. The wire turn cycle of corresponding closed PCB Rogowski coil 305 is composed of wiring 315 on the top layer, the through hole 320 and wiring 325 on the bottom layer. Wiring 330 on the bottom layer and wiring 315 on the top layer are pairs, same as through hole 335 and through hole 320, same as the wiring 340 on the top layer and wiring 325 on the bottom layer. These pairs are identical in position. It is the same with other wire turn cycles.
During the formation of combined PCB closed Rogowski coil 300, the closed PCB Rogowski coil 305 and closed PCB Rogowski coil 310 are stacked up on the upper and lower layers. The output ends 345 and 350 of the closed PCB Rogowski coil 305 are in the same position completely with the output ends 355 and 360 of the closed PCB Rogowski coil 310. Output end 350 of the closed PCB Rogowski coil 305 is connected with the output end 360 of the closed PCB Rogowski coil 310 to achieve the series connection of closed PCB Rogowski coil 305 and closed PCB Rogowski coil 310. Output end 365 of the combined PCB closed Rogowski coil 300 is connected with the output end 345 of closed Rogowski coil 305, and the output end 370 of combined PCB closed Rogowski coil 300 is connected with the output end 355 of the closed Rogowski coil 310.
When the AC interfering magnetic field vertical to page direction in FIG. 3 occurs, the interfering voltage signal generated between output ends 345 and 350 of the closed PCB Rogowski coil 305 and the interfering voltage signal generated between the output ends 355 and 360 of the closed PCB Rogowski coil 310 are approximately equal in size and opposite in polarity. Under the circumstance of the series connection of closed PCB Rogowski coil 305 and closed PCB Rogowski coil 310, the superposition of the two interfering signals is approximately zero. Therefore, when the AC interfering magnetic field vertical to page direction in FIG. 1 occurs, almost no interfering voltage signal will be generated between the output ends 365 and 370 of the combined PCB closed Rogowski coil 300.
Although the distance of the two closed PCB Rogowski coils used in the handling method is very close, the interference of the two coils caused by the external magnetic field cannot be in full coherence and cannot be offset completely. Further, the two closed Rogowski coils can be designed on single PCB to achieve the interference reduction of external magnetic field more effectively through the series connection of the two designed closed PCB Rogowski coils. FIG. 4A and FIG. 4B show the closed PCB Rogowski coil formed by the series connection of two groups of coils in opposite wiring direction on single PCB (refer to HIGH PRECISION ROGOWSKI COIL, U.S. Pat. No. 6,313,623 Nov. 6, 2001). FIG. 4A shows two groups of series-connected closed PCB Rogowski coils with opposite winding directions, whose wires are arranged on single PCB in a stagger way, and FIG. 4B shows two groups of series-connected closed PCB Rogowski coils with opposite winding directions, whose wires are arranged on single PCB in an interdigital way.
FIG. 4A and FIG. 4B show a scheme of the closed PCB Rogowski coil formed by the series connection of two groups of coils in opposite wiring direction on single PCB, although by which the interference of external magnetic field can be reduced more effectively, the two coils designed like this still fail to be the same completely, so the influence from the interference of external magnetic field cannot be removed well.
The opened Rogowski coil is composed of coils in two halves. When the opened Rogowski coil is used for current measurement of the alternating current I(t) to be measured in the current-carrying conductor, firstly the two halves of coils of the opened Rogowski coil are required to be opened to surround the current-carrying conductor, and then two halves of coils of the opened Rogowski coil are required to be closed to place the current-carrying conductor in center of the opened Rogowski coil after being closed. Current-carrying conductor is made to pass through the center of opened Rogowski coil vertically to ensure measurement accuracy with the centers of the current-carrying conductor and opened Rogowski coil in superposition. The current-carrying conductor is surrounded by the opened Rogowski coil. When the alternating current I(t) to be measured flows through the current-carrying conductor, it generates an AC magnetic field around the current-carrying conductor, and the magnetic lines are approximated as the circle centered in center of the current-carrying conductor.
The opened Rogowski coil also has the above-mentioned disadvantages of closed Rogowski coil that the two coils fail to be the same completely, so the influence from the interference of external magnetic field cannot be removed well.
Therefore, it is necessary to provide a more accordant PCB Rogowski coil with two groups of series-connected coils in opposite winding direction, capable of further reducing the influence on measurement caused by the external magnetic field and improving the capacity of interference resistance of PCB Rogowski coil.